The present invention relates to vacuum or pressure detectors. More particularly, the invention is directed to a detector and method for sensing a vehicle equipped with an onboard refueling vapor recovery system.
Gasoline gives off large amounts of vapor, caused by evaporation. This vapor contaminates the air and contributes to the formation of ground-level ozone. This ground-level ozone is caused by volatile organic compounds (VOCs) contained within the vapor of the gasoline. To combat these problems, the United States has mandated both a Phase I and a Phase II vapor recovery process.
Phase I vapor recovery is used during the refueling of gasoline storage tanks, such as at retail gasoline stations, to reduce hydrocarbon emissions. As shown in FIG. 1, Phase I therefore deals with the transfer of fuel from a delivery tanker 10 to an underground storage tank 12 of the gas station. Prior to the installation of Phase I vapor recovery systems, when a delivery truck transferred fuel to a storage tank at a gas station, the new fuel entering the storage tank would force accumulated gasoline vapors out of the tank and into the air, causing ground-level ozone. With a properly functioning Phase I vapor recovery system in place, each gallon of fuel transferred from the delivery tanker 10 into the storage tank 12 displaces a gallon of vapor. As shown in FIG. 1, this gallon of vapor is forced out of the underground storage tank 12 and back into the delivery truck 10 through a vapor recovery line 14. The recovered vapors in the tanker truck 10 can then be recycled and thus the emission of VOCs is reduced.
Phase II vapor recovery deals with refueling vehicles at the gas station. The same concepts apply to Phase II as to Phase 1. More specifically, when gasoline is delivered from the storage tank 12 at the gas station into the gas tank of a vehicle 16, accumulated gasoline vapors within the gas tank will be displaced by the fuel going into the tank. Phase II systems utilize a specially designed nozzle and hose system. Both the nozzle and hose have two passage-ways. As seen in FIG. 2, one passageway 18 is used to deliver gasoline to the vehicle 16 and the other passageway 20 is used for returning vapors from the vehicle fuel tank to the storage tank 12 of the gas station. As gasoline is pumped into the vehicle, vapors are forced out of the automobile fuel tank and through the vapor return hose back into the storage tank. There are now many locations which have installed Phase II vapor recovery systems.
The desire to reduce hydrocarbon emissions has been taken a step further. Federally mandated automobile-based controls for refueling emissions, onboard refueling vapor recovery (ORVR) systems, were introduced with many 1998 model year passenger vehicles. In a typical ORVR design, shown schematically in FIG. 3, the gasoline tank 22 of the vehicle 16 is provided with a narrow fill pipe 24. Fill pipe 24 narrows significantly from the nozzle inlet 26 to an interface 28 with the fuel tank. This narrowing allows for the formation of a continuous liquid seal as gasoline is pumped into the tank. This continuous liquid seal prevents hydrocarbon vapors from escaping the fuel tank while fuel is pumped into the tank. The vapors displaced by the addition of fuel into the tank are forced through a vent 30 connected to the tank 22. The vent 30 is then connected to a canister 32 that contains activated carbon. The carbon in the canister 32 captures and temporarily stores the hydrocarbon vapor. The ORVR vehicle is also equipped with a purge system which meters these captured hydrocarbon vapors to the vehicle engine as fuel. Typically, the purging process is completed with 30 miles of driving.
A difficulty has arisen that stems from the fact that the Phase II vapor recovery systems were designed for vehicles which were not equipped with ORVR systems. In other words, the Phase II vapor recovery systems are equipped to pull the vapors from the vehicle fuel tank into the facility storage tank. Therefore, the Phase II vapor recovery systems are designed to work with non-ORVR vehicles. A problem has arisen when a vehicle equipped with an ORVR system is presented to a facility having a Phase II recovery system. When a vehicle equipped with an ORVR system tries to fuel at a station equipped with a Phase II recovery system, the Phase II recovery system will attempt to pull vapor from the vehicle fuel tank. However, the ORVR system is designed to prevent the flow of vapors from the vehicle fuel tank by the formation of the continuous liquid seal. In the way that the typical ORVR system is designed, the ORVR system will thus not allow the Phase II recovery system to pull vapor from the vehicle fuel tank and vapor will be prevented from leaving the vehicle fuel tank.
When a Phase II vapor recovery system is designed, it is balanced so that the hydrocarbon vapor is pulled from the vehicle fuel tank at a rate equal to that at which fuel is being put into the system. When the Phase II vapor recovery system is prevented from pulling vapor from a vehicle fuel tank, one of two things will happen. In one instance, the Phase II vapor recovery system will continue to operate and will pull air rather than hydrocarbon vapor into the system. This air is lighter than the hydrocarbon vapor. Therefore, when air is being pulled into the facility storage tank instead of hydrocarbon vapor, a greater volume of air per timed unit is introduced into the system as compared to the volume of hydrocarbon vapor. This leaves the system out of balance and the greater volume of air increases the pressure in the underground storage tank. This increased pressure leads to fugitive omissions of hydrocarbon vapor. These emissions can occur in a variety of places due to the increased pressure, such as a vent pipe, and/or leaks through the tank top due to inadequate tank-top tightness. Therefore, if the Phase II vapor recovery system pulls air rather than hydrocarbon vapor, the basic goal of the system is defeated. More specifically, by pulling air into the underground storage tank, the pressure within the tank is increased and fugitive omissions of hydrocarbon vapor are released.
In a second instance, rather than pulling air through the system as opposed to hydrocarbon vapor, the system may merely shut off at the nozzle. This prevents the fuel dispensing nozzle from operating and is thus aggravating to the consumer. In this second instance, the consumer will be prevented from refueling his or her vehicle at the gas station merely because they have presented a vehicle having an ORVR system to a dispenser equipped with a Phase II vapor recovery system.
The above-described problems will continue as long as Phase II vapor recovery systems are present along with vehicles that are equipped with an ORVR system. Therefore, a detector is needed that can sense the presence of an ORVR equipped vehicle at the site having a Phase II vapor recovery system. Further, a method is needed that easily allows the detection of an ORVR equipped vehicle at a gas station having a Phase II vapor recovery system.